documents: drawn text reads back from its end, decoded as written

Each piece records how its source decodes: Markdown's escapes and
references for text, HTML's for an HTML block's runs, none for code
spans, cut as CommonMark cuts their end spaces. Matching runs from the
piece's end, so quote marks and indents at a line's start are never
taken for text, and an alert's text needs no moved position: alert()
takes no source again.

Lines split on LF, CRLF and CR alike; LineMap matches each drawn line
to the written line it ends once, so an HTML block maps in linear time
and a tab cut to spaces lands on the tab. A write-back refuses the
press when the pressed block's kind, text or drawing changed.

The hostile HTML test measures growth: a fixed 2 s budget failed under
the full suite's load on the old code too.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/documents/document/point.rs

@@ -3,11 +3,10 @@ use std::rc::Rc;
 use gpui::{Context, MouseButton, Window};
 use markdown::mdast;
 
-use super::{DocumentEvent, MarkdownDocument, edit::Landing, edit::moved};
+use super::{DocumentEvent, MarkdownDocument, edit::Landing, edit::moved, parse::Block};
 use crate::documents::{
     render::{OnPoint, Place, Pointed},
-    tree::lines_at,
-    tree::{alert, is_toc},
+    tree::{Node, alert, is_toc, lines_at},
 };
 
 /// A top-level block's kind.
@@ -36,7 +35,7 @@ impl TargetBlock {
             mdast::Node::Paragraph(_) if is_toc(node, source) => Self::Toc,
             mdast::Node::Paragraph(_) => Self::Paragraph,
             mdast::Node::Heading(heading) => Self::Heading(heading.depth),
-            mdast::Node::Blockquote(quote) if alert(quote, source).is_some() => Self::Alert,
+            mdast::Node::Blockquote(quote) if alert(quote).is_some() => Self::Alert,
             mdast::Node::Blockquote(_) => Self::Quote,
             mdast::Node::List(_) => Self::List,
             mdast::Node::Code(_) => Self::Code,
@@ -95,6 +94,12 @@ impl MarkdownDocument {
         })
     }
 
+    /// A block's kind, text and what it draws.
+    fn drawn(&self, block: &Block) -> (TargetBlock, String, Option<Vec<Node>>) {
+        let text = self.parsed.text[block.range.clone()].to_string();
+        (block.kind, text, block.nodes.clone())
+    }
+
     /// Caret to `at`, else block `ix`; the owner hears.
     pub(super) fn point(
         &mut self,
@@ -109,7 +114,7 @@ impl MarkdownDocument {
             block => block.flatten(),
         };
         let kind = block.map(|block| block.kind);
-        let pressed = block.map(|block| self.parsed.text[block.range.clone()].to_string());
+        let pressed = block.map(|block| self.drawn(block));
         let at = at.or(block.map(|block| block.range.start));
         let written = self.commit(cx);
         if written.is_some() {
@@ -128,7 +133,7 @@ impl MarkdownDocument {
         // A write-back may change the pressed block.
         let now = (self.parsed.blocks.iter())
             .find(|block| block.range.start <= at && at <= block.range.end)
-            .map(|block| self.parsed.text[block.range.clone()].to_string());
+            .map(|block| self.drawn(block));
         if written.is_some() && pressed.is_some() && now != pressed {
             return log::warn!("markdown document: the write-back changed the pressed block");
         }